Abd al-Razzaq (may Allah have mercy on him) says: I heard a man ask al-Thawri (may Allah have mercy on him): Who are the family of Muhammad? He said: People have differed about this. Some say that the household is meant, and some say: whoever obeyed him (peace and blessings be upon him) and acted upon his Sunnah.
Abu Bakr says: I think Abd al-Razzaq (may Allah have mercy on him) said: 'whoever obeyed him'.
Imam al-Bayhaqi (may Allah have mercy on him) says: Whoever holds this second view would most likely argue that Allah Almighty said to Sayyiduna Nuh (peace be upon him): "Load into it a pair of every kind, and your family" [Surah Hud: 40], and he said: "My Lord, indeed my son is of my family, and Your promise is true, and You are the most just of judges." (Allah) said: "O Nuh, he is not of your family; indeed, his deeds are not righteous" [Surah Hud: 45-46]. So Allah excluded the son of Sayyiduna Nuh (peace be upon him) from the family of Nuh (peace be upon him) because of shirk.
Imam al-Shafi'i (may Allah have mercy on him) answered this by saying that the words of Allah, the Blessed and Exalted, "He is not of your family" [Surah Hud: 46] do not mean what has been stated; rather, they mean that he was not among those fit to board the Ark. Allah Almighty said: "And load your family into the Ark, except those concerning whom the decree of destruction has already gone forth." [Surah Hud: 40]
This verse too makes clear that the son of Sayyiduna Nuh (peace be upon him) was of his family, and the reason he did not board the Ark was that his deeds were not right.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2869
Sayyiduna Wathilah bin al-Asqa' al-Laythi (may Allah be pleased with him) says: I wanted to meet Sayyiduna Ali (may Allah be pleased with him), but he was not there, so Sayyidah Fatimah (may Allah be pleased with her) said: He has gone to the Messenger of Allah (peace and blessings be upon him) to invite him. Do sit here. Then Sayyiduna Ali (may Allah be pleased with him) came with the Messenger of Allah (peace and blessings be upon him) and they went inside, and I too went in with them. The Messenger of Allah (peace and blessings be upon him) called Hasan and Husayn (may Allah be pleased with them both), seated both of them on his lap, and seated Fatimah (may Allah be pleased with her) and her husband close to himself. Then he put his cloak over them. I was to one side. Then he (peace and blessings be upon him) said: "Allah only wishes to remove impurity from you, O people of the household, and to purify you thoroughly [Surah al-Ahzab: 33]. O Allah, these are my family; O Allah, my family are most deserving." Wathilah (may Allah be pleased with him) says: I said: O Messenger of Allah, am I also of your family? He (peace and blessings be upon him) said: "Yes, you too are of my family." Wathilah (may Allah be pleased with him) says: That is among the greatest things I hope for.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2870
(a) This same hadith is reported from Wathilah bin al-Asqa' (may Allah be pleased with him) through another chain, and its chain too is sahih (authentic).
(b) In the above hadith, Wathilah's (may Allah be pleased with him) being of the family is particular to him; establishing it for the whole Ummah is far-fetched. And calling Wathilah (may Allah be pleased with him) family is also by way of resemblance, not in the true sense.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2871
Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) says that (what is meant by) the family of Muhammad (peace and blessings be upon him) is his Ummah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2872
Abu Hurmuz Nafi' (may Allah have mercy on him) says: I heard Sayyiduna Anas bin Malik (may Allah be pleased with him) say that someone asked the Messenger of Allah (peace and blessings be upon him): "Who are the family of Muhammad?" He (peace and blessings be upon him) said: "Every God-fearing person is of the family of Muhammad."
It is not valid to use this hadith as evidence. Nafi' al-Sulami Abu Hurmuz, of Busra, was declared a liar by Yahya bin Ma'in, and Ahmad bin Hanbal and other huffaz declared him da'if (weak).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2873